I have been running Lightroom 5 since 5.1. I currently have been running the newest version 5.7 since it was released. About 2 weeks ago I noticed a significant performance drop off. It happened when I started going back through and changing keywords on large batches. Now it continues when I'm changing keywords on as little as 1 photo. My library has 54000+ photos but previously i had no issues with that quantity. I have optimized the catalog several times. Sometimes i have to wait upto 1 1/2 minutes for everything to apply. Any suggestions?

One longshot to try: In the Metadata panel, make sure the current tagset is set to Default and that the panel is closed. When it's set to others, such as EXIF and IPTC, LR can take a relatively longer time recomputing the metadata values to display, such that changing the selection is very sluggish.